1. Field of the Invention
This invention relates to an LED lamp having an envelope of an improved shape.
2. Description of the Related Art
FIG. 1 shows the envelope of a conventional LED lamp having more than two semiconductor chips. In the figure, reference numeral 1 denotes semiconductor chips, reference numeral 2 leads, reference numeral 3 bonding wires, reference numeral 4 an envelope made of a translucent resin and having a spherical portion denoted by reference numeral 5, and reference numeral 6 the axis of the envelope.
As is shown in FIG. 1, the envelope 4 can be divided mainly into an upper portion and a lower portion. The upper portion has, for example, a single curved surface which is formed of part of a spheroid or sphere having a rotational axis which coincides with the axis 6. The lower portion is cylindrical and coaxial with the upper portion. The curved surface serves as the lens of the LED lamp.
With this structure, however, all the semiconductor chips cannot be located on the focus of the lens. Thus, as is shown in FIG. 4, the light beams emitted from the lamp are inevitably separated from each other.